This invention relates generally to gas turbine engines, and more specifically to a gas turbine engine rotor blade having improved tip cooling.
In general, a gas turbine engine includes one or more turbine blade rows disposed downstream of a combustor for extracting energy from combustion gases. A stator shroud is disposed radially outwardly of the rotor blade tips. A relatively small clearance is provided between the blade tips and the stator shroud to reduce leakage of the combustion gases over the blade tips during operation. The clearance between the blade tips and the stator shroud must nevertheless be adequate to minimize the occurrence of blade tip rubs during operation. Each of the rotor blades includes conventionally known pressure and suction sides which are preferentially aerodynamically contoured for extracting energy from the combustion gases.
Conventionally, the blades, including the blade tips, are cooled by channeling a portion of the compressed air from the gas turbine compressor through hollow turbine blades. Compressed air diverted to cool the blades is then not available for combustion in the combustor, decreasing engine efficiency.
Prior art turbine blade tips are particularly susceptible to the damaging effects of the hot combustion gases such as blade tip distress by oxidation and thermal fatigue. Erosion of the blade tip adversely affects the aerodynamic performance efficiency of the blade. Also, increases in the tip clearance results in decreased efficiency.
Blade cooling configurations may include film-cooling apertures extending through the blade pressure and suction sidewalls for channeling the cooling air from inside the blade to the outer surfaces to provide conventional film cooling thereof.
A known blade design includes a tip shelf extending along a first side of an airfoil, see for example, U.S. Pat. No. 5,261,789. A plurality of generally radially extending cooling holes is disposed through the tip shelf in flow communication with an interior flow channel to channel cooling air toward the blade tip.
Although previously known designs provide improvements in tip cooling, turbine blade tips remain susceptible to cracking due to thermal distress.
Accordingly, it is desirable to have improvements in blade tip cooling to improve operational performance and increase service life by reducing thermal fatigue.